This invention relates in general to power plants having steam turbines, steam surface condensers, and makeup water. Specifically, the invention relates to steam surface condenser apparatus which condense steam flowing out of the exhaust of the steam turbines and to methods of deaeration of makeup water.
In power plant applications with steam as the drive fluid, condensate loses in the cycle are compensated by the addition of the makeup water. Normally, demineralized makeup water saturated with air is admitted in the steam surface condenser. The steam surface condenser is expected to deaerate the makeup water. In most instances, the makeup flowrate into the condenser is small, approximately 1% of the turbine exhaust steam flow rate. Such small flow rates of makeup water can be adequately deaerated in the condenser without the use of any special hardware.
In certain applications, depending upon the cycle requirements, large amounts of makeup water can be admitted into the condenser. The makeup water flowrate can be as high as 20%-30% of the steam flow rate. Deaeration of large quantities of makeup water is carried out in special hardware located external to the steam surface condenser. External vacuum deaerators utilizing spray and tray heating are commonly used for deaeration of makeup water in many applications. In an external vacuum deaerator, the makeup water is sprayed in a cylindrical shaped vessel. Turbine exhaust steam is admitted into the cylindrical shaped vessel from the lower side. The makeup water comes in contact with turbine exhaust steam, gets heated, and liberates the dissolved air. The make up water then falls through a series of trays located in the lower section of the cylindrical shaped vessel, effecting further deaeration.
The use of external deaerators has several known disadvantages, not the least among them being the amount of real estate space taken up, the need to inspect, operate, and maintain the a separate piece of hardware. There has been a long felt need in this art to provide a way to deaerate the make up water internal to the condenser and reduce or eliminate the external makeup water deaerators.
It is an object of the present invention to provide an improved method and apparatus for introducing makeup water to a steam surface condenser and deaerating the makeup water.
It is a further object to reduce the size or eliminate entirely the external deaerators used with steam surface condensers in steam turbine power plant applications.
These objects, and others which will become apparent from the following disclosure and drawings, are achieved by the present invention which comprises in one aspect deaeration of large quantity of cold makeup water, saturated with air, by the use of a two stage deaeration technique wherein the entire deaeration hardware is located inside the condenser.
The power plant apparatus of the invention comprises a condenser for condensing turbine exhaust steam having a steam dome, a steam inlet, a tube bundle, a hot well for collecting condensate, an air removal section, an internal makeup water heater bundle, and apparatus to introduce makeup water into said steam dome. The preferred apparatus to introduce makeup water into the steam dome is an internal makeup water header which is a pipe having spray nozzles which, most preferably, are self adjusting.
The spray nozzles are arranged, in most embodiments, counter-currently to the flow of steam introduced by the steam inlet. The system preferably extracts air at the outlet of the internal makeup water heater bundle.
The makeup water heater bundle, located internal to the steam dome, comprises preferably of a series of U-tubes.
The local air extraction can be performed by a air evacuation device or automatic air release valve at the outlet of the internal makeup water heater bundle.
According to the process aspect of the invention, a makeup water heater bundle section is arranged within the condenser and the resultant heated makeup water is introduced into the path of the turbine exhaust steam within the steam dome. In the makeup water heater bundle, the makeup water is preferably heated to a temperature of 5.0xc2x0 F. below the saturation temperature of the turbine exhaust steam section. The makeup water is further heated to the saturation temperature of the turbine exhaust steam by direct contact.
The air liberated from the makeup water in the bundle section is preferably automatically and periodically vented prior to introducing the resultant heated makeup water into the condenser.
The resultant heated makeup water is introduced using spray nozzles in a direction countercurrent to the turbine exhaust stream in a preferred process of the invention. In general, it is preferred that the spray nozzles are arranged so as to maximize the contact time between the turbine exhaust steam and the makeup water.
It is further preferred to provide an oversized air cooling zone in the said condenser so as to improve the venting capability.
A hooded air channel within the condenser may be provided to prevent dripping condensate from coming in contact with the air-vapor mixture.